降低等效串聯電感效應之延遲漣波重建的固定導通時間控制於使用陶瓷電容的降壓電源轉換器

Abstract

此論文提出一應用於固定導通時間控制之切換式電源轉換器並使用積層陶瓷電容的具高雜訊邊限之差動零點補償器技術。由於低成本的優點與等效串聯電阻小的特性，積層陶瓷電容目前被廣泛的使用於消費性電源管理晶片。然而，固定導通時間控制法將因為輸出電容與其等效串聯電阻之乘積所得的時間常數太小，致使系統遭遇到次諧波震盪的穩定性問題。但反觀大的等效串聯電阻雖然可以確保系統穩定性，卻也犧牲了輸出電壓在暫態反應的品質。因此，具高雜訊邊限之差動零點補償器在此被提出以降低時間常數的限制，並提高系統對等效串聯電感的效應之容忍度。同時，此技術的使用不需增加額外的晶片腳位，也不會提高電物的複雜度。除此之外，更提出一自我補償之固定導通產生器以利提供高線性度的變化維持更穩定的操作頻率。積層陶瓷電容的使用，使得漣波大小在輸出負載滿載8安培的狀況下被降低僅剩8毫伏特。等效串聯電阻也使系統有91%的高效率。穩定條件的分析與模擬結果都說明了在1毫歐姆的等效串聯電阻的使用仍可以保持系統的穩定性。晶片的實際量測結果也成功驗證補償方法的正確性。在如此的條件下，相較於傳統的固定導通時間控制法，系統可操作的切換頻率限制從2 MHz被大大將低至250 KHz並提供高效率效能表現。

A differential-zero compensator with the noise margin enhancement (DZC-NME) technique in constant on-time control buck DC-DC converter with ceramic output capacitor is proposed in this thesis. Ceramic capacitors are widely used in commercial power management ICs due to the advantages of low cost and equivalent series resistance (ESR). However, the stability often confronts with the sub-harmonic problem caused by small time constant, which is the product of the output capacitor and the ESR. Contrarily, the output capacitor with large ESR can ensure the system stability but suffers from large transient voltage and cost issue. Thus, the proposed DZC-NME technology eliminates the constraint of large time constant and simultaneously tolerates the existence of equivalent series inductor (ESL) effect. That is, it remits the limitation without adding extra pins and increasing the circuit complexity. Furthermore, the proposed self-compensated on-time timer (ONT) offers the reliable on-time period with improved linearity. Besides, utilizing ceramic capacitor derives smaller ripple of 8mV at full-load condition, 8A. High efficiency of 91 % can be guaranteed due to the small ESR value. Moreover, stability criteria analysis and simulation results demonstrate that the stability can be ensured even if the ESR is small than 1mΩ. Experimental results demonstrate the function of compensation even at transient condition. Compared with the conventional design, the limitation of lowest switching frequency is released from 2 MHz to 250 KHz to guarantee high efficiency. In other words, the performance of the buck DC-DC converter with the constant on-time control is improved significantly